1. Field of the Invention
The present invention relates to a method of mechanically removing scales (oxidizing film) on the surface of a metal wire and an apparatus thereof, and particularly to a quite new descaling technique of removing scales of a metal wire by imparting a torsion to the metal wire.
2. Description of the Related Art
A hot-rolled wire or a metal wire in the course of processing such as patenting is exposed to an oxidizing atmosphere at a high temperature by an intermediate heat-treatment performed in the manufacturing process, and thereby it is stuck with scales on the surface. The scales must be perfectly removed because they cause, for example, the seizure of a die in the subsequent drawing process.
The scales are removed by a chemical method (acid pickling) and mechanical method (mechanical descaling). The former, however, has been not prevailed so much because it must be provided with a waste liquid treatment equipment for eliminating pollution problems. On the contrary, the latter has come to be extensively applied because it does not require any waste liquid treatment equipment. In general, there have been known two mechanical descaling methods: (1) a reverse bending method of allowing a running wire to pass through several rollers for repeatedly bending/returning it; and (2) a shot blasting method of acceleratively jetting small particles from a nozzle using compressed air for blasting them on the surface of the metal wire.
The above-described methods, however, have the following disadvantages. For example, in the reverse bending method, the repeated bending/returning cannot be uniformly applied to a metal wire along its whole periphery, and thereby untreated scales remain on part of the surface of the metal wire.
FIG. 17 is a view illustrating the whole concept of the reverse bending method. A metal wire 5 runs from the left to the right in a box 6. The interior of the box 6 is partitioned into a reverse bending portion 8 and a brushing portion 9 by means of a partitioning plate 7. The metal wire 5 is bent in the different directions in the course of passing through a group of rollers (first roller 1, second roller 2, third roller 3 and fourth roller 4 disposed in this order). Namely, scales are removed using a different in toughness between the metal wire 5 and scales. At the brushing portion 9, residual scales are removed using wire wheels. Next, the metal wire 5 discharged from the box 6 is, for example, drawn through a die (not shown).
FIGS. 18A to 18F are views each illustrating the contact state between the metal wire 5 and each of the rollers 1 to 4, seen from front side or upper side of the apparatus shown in FIG. 17. Referring to FIG. 18A (seen from the front side), the upper peripheral surface (shown by the mark .circle-solid.) of the metal wire 5 is press-contacted with a lower side peripheral surface la of a first roller 1, and both side peripheral surfaces (shown by the marks .tangle-solidup., .DELTA.) are not contacted with the peripheral surface of the roller.
Next, in FIG. 18B (seen from the front side), since the axial center of the second roller 2 is disposed to be in parallel to the axial center of the first roller 1, the metal wire 5 is bent in the direction reversed to the bending direction by the first roller 1. As a result, the portion shown by the mark .smallcircle. on the sided opposed to the portion shown by the mark .circle-solid. is contacted with an outer peripheral surface 2a of the second roller 2. FIG. 18C shows the second roller 2 from the upper side, in which the portion shown by the mark .smallcircle. is contacted with the outer peripheral surface 2a of the second roller 2. In FIG. 18D (seen from the upper side), the metal wire 5 is shifted from the second roller 2 to the third roller 3.
The second roller 2 is disposed such that the axial center is perpendicular to that of the third roller 3. The reason for this is that in the case where the metal wire 5 runs between the rollers in parallel to each other as shown in the first and second rollers 1 and 2, the contact point of the metal wire 5 with the roller is repeatedly shifted only between the portions shown by the marks .circle-solid. and .smallcircle., that is, the metal wire 5 is repeatedly bent only in the reversed directions. As a result, the contact point is not changed into the portions shown by the marks .tangle-solidup. and .DELTA., to limit the scale removing directions, thus causing a fear that non-treated portions remain. In the actual operation, however, since the metal wire 5 is already imparted with the bending deformation in the specified direction, and exhibits a large resistance against the bending along the other direction. For this reason, the metal wire 5 is simply twisted by 90.degree. while being restricted in the outer groove of each of the rollers 2, 3. Accordingly, the metal wire 5 is apparently turned by 90.degree. clockwise (horizontal direction in the figure) by the twisting effect of -90.degree. against the bending by 180.degree., and in such a state, it reaches the third roller 3. Consequently, in FIG. 18D (seen from the upper side), the portion shown by the mark .circle-solid. of the metal wire 5 is closely contacted with an outer peripheral surface 3a of the roller. In this way, in the case of the actual reverse bending operation, there occurs an inconvenience that the contact point with the outer peripheral surface of the roller is not satisfactorily changed.
Moreover, in FIG. 18E in which the fourth roller 4 is disposed such that the axial center thereof is perpendicular to that of the third roller 3, the metal wire 5 is apparently turned by 90.degree. counterclockwise (vertical direction in the figure) by the twisting effect of +90.degree. against the bending by 180.degree., and in such state, it reaches the fourth roller 4. Consequently, in FIG. 18E (seen from the upper side) and FIG. 18F (seen from the front side), the portion shown by the mark .smallcircle. is contacted with a peripheral surface 4a of the roller, and consequently, the contact point is not also changed into the portion shown by the marks .tangle-solidup. and .DELTA.. Thus, in the course where the metal wire 5 is carried from the first roller 1 to the fourth roller 4, it is usually subjected to the repeated bending within the same surface, which causes a serious disadvantage in which the removable of scales is limited to a specified portion.
On the other hand, the shot blasting method is high in scale removing effect as compared with the reverse bending method, but it is disadvantageous in that the blasting efficiency to a metal wire having a small diameter is low and that the equipment cost is increased.
On the other hand, the method of forcibly applying a displacement such as bending to the metal wire 5 requires a means for preventing the propagation of the return action of the displacement. In general, the means includes a press-contact rollers 63, 64 and 65, each having a small diameter, disposed between pinch rollers 61 and 62 as shown in FIG. 19. In this means, however, since the diameter of each roller is small, the contact area between a metal wire and each press-contact roller cannot be sufficiently ensured, so that the contact pressure between the metal wire and the press-contact roller is excessively increased and thereby the metal wire come to be contacted with the press-contact roller nearly at one point. As a result, there is a fear that scratches are generated on the surface of the metal wire. Accordingly, a technique of certainly preventing the propagation of the return action of the displacement has been required.
The metal wire subjected to mechanical descaling is fed to the subsequent process, for example, drawing process. In this case, since the drawing rate of the metal wire is not constant, the method of imparting a single displacement amount fails to uniformly remove scales. Namely, in the actual operation, it is necessary to examine a variation in the running speed of a metal wire.